1. Field of the Invention
The invention relates to a ladder, a combined ladder and a step ladder, and more particularly to an extension ladder, a combined extension ladder and a step ladder.
2. Description of the Related Art
Extension ladders, combined extension ladders and step ladders are widely used nowadays. However, there are several problems with them: firstly, they have complex structure, single functions, and poor extension performance; secondly, they are difficult to be combined; finally, they lack safety and incorrect operation thereof often hurt operators.